FOR SELECT ... INTO ... DO

Description: Executes a SELECT statement and retrieves the result set. In each iteration of the loop, the field values of the current row are copied into
local variables. Adding an AS CURSOR clause enables positioned deletes and updates. FOR SELECT statements may be nested.

The SELECT statement may contain named SQL parameters, like in “select name || :sfx from names where number = :num”. Each parameter must be a PSQL variable that has been declared previously (this includes any in/out params of the PSQL module).

Caution! If the value of a PSQL variable that is used in the SELECT statement changes during execution of the loop, the statement may (but will not always) be re-evaluated for the remaining rows. In general, this situation should be avoided. If you really
need this behaviour, test your code thoroughly and make sure you know how variable changes affect the outcome. Also be advised
that the behaviour may depend on the query plan, in particular the use of indices. As it is currently not strictly defined,
it may change in some future version of Firebird.

create procedure relfields
returns (relation char(32), pos int, field char(32))
as
begin
for select rdb$relation_name from rdb$relations
into :relation
do
begin
for select rdb$field_position + 1, rdb$field_name
from rdb$relation_fields
where rdb$relation_name = :relation
order by rdb$field_position
into :pos, :field
do
begin
if (pos = 2) then relation = ' "'; -- for nicer output
suspend;
end
end
end

AS CURSOR clause

Available in: PSQL

Added in: IB

Description: The optional AS CURSOR clause creates a named cursor that can be referenced (after WHERE CURRENT OF) within the FOR SELECT loop in order to update or delete the current row. This feature was already added in InterBase, but not mentioned in the
Language Reference.

Example:

create procedure deltown (towntodelete varchar(24))
returns (town varchar(24), pop int)
as
begin
for select town, pop from towns into :town, :pop as cursor tcur do
begin
if (town = towntodelete)
then delete from towns where current of tcur;
else suspend;
end
end

Notes:

A “FOR UPDATE” clause is allowed in the SELECT statement., but not required for a positioned update or delete to succeed.

Make sure that cursor names defined here do not clash with any names created earlier on in DECLARE CURSOR statements.

AS CURSOR is not supported in FOR EXECUTE STATEMENT loops, even if the statement to execute is a suitable SELECT query.